1. Field of the Invention
The present invention relates to a sensor apparatus for detecting a positional relationship between two members arranged in opposed relation to each other, using a change in electrostatic capacitance between electrodes of the respective members and a method used for the sensor apparatus.
2. Description of the Related Art
In recent years, a proximity sensor of electrostatic capacitance detection type has been proposed for detecting a proximity of an object (JP-A 2008-192319 (KOKAI)). In this sensor of electrostatic capacitance type, a first member constituting an object of detection and a second member of the sensor part have first and second electrodes, respectively, which are so arranged as to be opposed to each other. Of these electrodes, the one arranged on the first member is supplied with an electrical signal. The sensor detects a change in electrostatic capacitance between the first and second electrodes using the electrode arranged on the second member, thereby detecting a relative positional change of the members.
The sensor apparatus for detecting the proximity between two members is used for electronic devices such as a mobile phone. In the mobile phone, for example, the power consumption is required to be suppressed as far as possible to permit the use for a long time. In a conventional magnetic sensor apparatus, the positional relationship between a magnet and a Hall element. The magnet is arranged on a first member constituting an object of detection. The Hall element is arranged on a second member constituting a sensor part. In the process, the magnetic sensor apparatus detects a magnetic field from the magnet by driving the Hall element intermittently with a predetermined period. As a result, the power consumption of the sensor apparatus is suppressed and a waste of a battery power can be reduced.
As described above, if the electronic devices are required to suppress the power consumption, it is desirable for the sensor apparatus for detecting the proximity between two members to be operated intermittently so as to suppress the waste of the battery power. In the sensor apparatus of electrostatic capacitance detection type, however, the object of detection and the sensor part are operated independently of each other. This poses the problem that an attempt to operate the sensor apparatus intermittently fails to detect the relative positions of the members successfully due to the different intermittent operations between the object of detection and the sensor part.
As understood from the foregoing description, the intermittent operation of the sensor apparatus of electrostatic capacitance detection type harbors the problem that the relative positions of the members cannot be successfully detected in the case where the intermittent operation of the object of detection and that of the sensor part are different from each other.